In television broadcasting services (including both wireless and cabled transfer), the present invention relates to a method enabling the watching of normal TV pictures restored to be so by a prescribed means (descrambling) while it may not be possible to do so by reception of the broadcast images directly. More particularly the present invention relates to a TV picture scrambling method making possible the transfer of TV pictures, by means of key and address signals combined into selected video signals upon generating key signals to be used for restoring later TV pictures as they will have been received, and address signals permitting terminal equipment to receive said program.
In conventional TV broadcasting services, either by wireless or cable, programs can be watched on normal, standard TV sets, within respective areas covered by service networks, by reproducing TV pictures as received. However, it is necessary to make it possible to view TV programs only on TV sets owned by specific subscribers, but not by others with respect to paid TV broadcasting services. Particularly, in CATV broadcasting services capable of providing various programs, the operation of such CATV stations is dependent on the fees paid for programs, so that the segregation of subscribers is essential. For that reason, transmitters of programs require a scrambling method which manipulates the pictures transmitted so that they cannot be reproduced as normal pictures if received as they are.
Firstly, a CATV system will be outlined hereunder with reference to FIG. 1.
This system has a unique chargeable program broadcasting function.
FIG. 1 shows the entire CATV system. This system comprises a center 1 and thousands and thousands of terminal equipment units 28 connected therewith by means of coaxial cables. From the center 1 is laid a trunk line cable 3 on which are installed at predetermined points a trunk line amplifiar 4 and a branch box, respectively. From this branch box 5 are drawn a plurality of branch cables 6, and each branch cable 6 is provided at predetermined points with a branch amplifier 7 and a tapoff 8, respectively. From each tapoff 8 are drawn plurality of sub-branch cables 9; each terminal thereof is drawn into a household 2. The terminal equipment 28 in each household 2 comprises a main box 10, a TV set 11 and a control box 12. The terminal of a sub-branch cable 9 is connected to the main box 10, the TV set 11 and the control box 12. That is, the center 1 and every terminal unit 28 in subdivisioned households are interconnected in a Christmas tree manner.
Outside the aforementioned center 1 is erected a receiving antenna 13, and this is connected to a demodulator in a source group 14. In this source group are a video-disc player 16, video-tape recorder 17, studio 18 and so forth. A modulation transmitting part 19 that receives signals from the source group 14 comprises two systems: one consists of an IF modulator circuit 20, a scrambling circuit 21 and an up converter circuit 22; and the other, an IF modulator circuit 23 and an up converter circuit 24. Respective outputs from the up converter circuits 22 and 24 are connected to the trunk line cable 3. The trunk line cable 3 is also connected to a data transmitter/receiver set 25 that communicates with each main box 10. To the data transmitter/receiver set 25 is connected a computer 26 to which is connected peripheral equipment 27 including a printer, display, etc.
The operation of this CATV system will now be described. Turning ON the TV set 11 and operating the control box 12 to select a desired channel enables pictures to be supplied to the TV set 11 through conversion, by means of the main box 10, of a frequency for said channel into that for an idle channel. Type of channels selectable by means of the control box 12 comprise:
(A) retransmissions for receiving programs as they are; PA1 (B) self-sustained programs (free of charge); and PA1 (c) chargeable programs. Each group has several channels, respectively, thus making a total of some 20-30 or more selections available.